I'm trying to fix a busted slip joint nut on my p-trap in my bathroom sink. The nut's top basically started leaking and came apart (corrosion?) when I tried to loosen and replace. The top is shown in the picture where it says "busted slip joint nut". I didn't think it would be a problem to fix (simply buy new nuts). However, I unscrewed the part of the pipe that goes into the wall hoping can take the pipe out (which is required to get the new slip joint nut on, and take the top of the old one off) but there is some sort of seal/binder, labeled in the picture as "blue stuff", and the pipe is not budging at all. How do I safely remove the pipe to get the new slip join nut on?? Once I do, I'm guessing I have to re-seal. What is the stuff called that I need? I'm obviously a rookie at this sort of stuff so descriptions in layman's terms are greatly appreciated. I'd hate to call a plumber for something an average joe can do for $20 parts. (Image wasn't showing, so here is the link to the image, the link will not download anything, etc., it will just show the image of the pipe): http://postimg.org/image/6st97tsnr/